Electromagnetic relay control

ABSTRACT

The process for controlling an electromagnetic relay comprises at least one contact, controlled by a voltage or current supply. In accordance with the invention the control is modulated according to the voltage or current supply, to the contacting voltage required to close the contact of the relay, and to the maintaining voltage which is sufficient to maintain this closure.

The invention concerns the area of electromagnetic relays. It relates inparticular to the relays used in automobile vehicles.

In order to be active, the coils of electromagnetic relays are suppliedwith power directly by a battery or any other power source provided tocontrol a contact.

This is particularly the case with electromagnetic relays fitted to thevarious electrical or electronic service boxes (BSE) of automobilevehicles. These are for example engine monitoring boxes (BSM),intelligent service boxes (BSI) or even central cabin units (UCH) orengine units (USM).

These boxes are of limited volume and generally have a certain number ofelectromagnetic relays with other electrical or electronic components,the assembly being intended to ensure calculation and switchingfunctions.

In order to control an electromagnetic relay, in particular in order toclose the contact, it must be supplied with sufficient power, i.e. aso-called contact-contacting voltage must be applied to its coil. Thisvoltage is substantially greater than the so-called maintaining voltagerequired simply to maintain it in the contacted state. In order to openthe contact a voltage is applied which is necessarily lower than theso-called release voltage.

The voltage applied across an electromagnetic relay coil generates acurrent exciting an electromagnet which closes the contact of the relayor keeps it closed. The coil then dissipates thermal energy, of theorder of several watts, by the Joule effect. The contact itself, whenclosed, permits passage of an electric current and also dissipatesthermal energy, slightly lower than the previous energy level.

In order to control the relays, the battery voltage of the vehicle iscurrently applied in the boxes. This voltage varies over time.

In order to overcome this disadvantage the document U.S. Pat. No.5,930,104 proposes a device permitting the control voltage of a relay tobe maintained at a minimum level required for its operation, and controlthereof to be suspended when this voltage is greater than the maximumthreshold admissible by its coil.

However, a BSE box can comprise up to about ten relays having variouscharacteristics. The thermal constraints imposed on the service boxes bymanufacturers have become very severe. Since the density of theinstalled components continues to increase, these constraints are moreand more difficult to respect and, for obvious reasons of safety, it isnot possible to suspend the control of certain BSE box relays if theircoil can no longer sustain the supply voltage.

An object of the invention is to provide a control process permittingthe relays to operate in acceptable thermal and operational conditionsand to do so in a confined environment as described above.

In accordance with the invention the process for controllingelectromagnetic relays, controlled by a current or voltage supply, ischaracterised in that the control is modulated according to the currentor voltage supply and to the contacting voltage which is sufficient toclose the contacts of the relay, and is modulated according to thecurrent or voltage supply and to the maintaining voltage which issufficient to maintain this closure.

By this process the coil of the relay dissipates only a level of thermalenergy reduced to the minimum necessary both to close the contacts ofthe relay and to maintain this closure. It is no longer necessary tosuspend the control of the relay in the event of excessively high supplyvoltage.

The invention also relates to a device for controlling anelectromagnetic relay from a voltage source. It is characterised in thatit has a module for adapting the power supply of the relay and a controlmodule to control the power supply-adapting module.

It is thus possible to supply the relay with levels of energy justnecessary during contacting and during maintaining of its contacts,which makes it possible to obtain a reduction in the thermal dissipationof its coil.

The control module preferably has means to control the duration ofoperation of the power supply-adapting module during contacting of thecontacts, a duration at the end of which it must control the maintainingof the contacts. These means take account in particular of the type ofrelay controlled.

It is also preferable that the control module has a module for detectingmicro power cuts in order, at the end of a micro power cut in the supplyvoltage of the relays, to control, upon closure, the relays if they wereclosed before the micro power cut.

It is another preferable feature that the control device comprises anoscillator connected to the power supply-adapting module, whichcomprises a calculation function and a pulse duration modulation (MID)function for the supply voltage. In this way different contacting andmaintaining commands are obtained by simply changing the cyclic ratio(RC) of the MID function.

The energy dissipated by the coil thus controlled depends on the ratioRC imposed by the MID function. In particular, at equal supply voltage,the cyclic ratio RC imposed by the calculation function duringmaintaining is lower than that imposed during contacting of the relay.

The invention will be better understood with the aid of the followingdescription and the accompanying drawings in which:

FIG. 1 illustrates a functional block diagram of a control device for arelay in accordance with the invention,

FIG. 2 illustrates a typical timing diagram of the control applied to arelay by the device of the invention,

FIG. 3 illustrates an example of implementation of the invention for aservice box,

FIG. 4 illustrates a timing diagram of the operation of the MID in theprevious implementation.

With reference to FIG. 1, the continuous supply 1, in this case abattery, of which the voltage V_(A) can vary, depending on its use at aparticular moment, between 9 and 16 volts, supplies:

a relay 2 when a serviceable voltage U is cut,

an analogue digital converter 4 supplying the momentary value V_(A),

a control-command unit 3 for the serviceable voltage U and

a device 10 for control of the relay 2.

The device 10 comprises for this purpose a control module 11 whichreceives a command issued by the control-command unit 3 and whichcontrols a power supply-adapting module 12. It also comprises anoscillator 13 which delivers a frequency of 20 kHz to the module 12.

The module 11 comprises a circuit 111 for detecting micro power cuts, aclock 112 and a memory 113 containing the characteristics of the relay2.

The module 12 comprises a means 122 for pulse duration modulation,designated by the initials MID or by the abbreviation PWM for “pulsewidth modulation”. It receive its instructions from a calculation andcontrol means 123 by its MID circuit [lacuna] the switch I when thepower supply of the relay 2 is cut.

The operation of the device will now be explained.

The switch I being open, the relay 2 is at rest, contact open (it willbe assumed at this point that this is a “working” contact relay). Inorder to close the contact of the relay 2, the control-command unit 3sends a closure command to the device 10, more precisely to its controlmodule 11.

The module 10 reads the characteristics of the relay in its memory 113.These are the contacting voltage V_(C), the maintaining voltage V_(M) tobe respected and the minimum duration over which the voltage V_(C) mustbe applied to contact the contact securely. This duration is representedby Δt in FIG. 2.

The module 11 then sends a closure command (OF) from the relay 2 to thepower supply-adapting module 12. At the same time, it triggers its clock112 for a time Δt, at the end of which it sends to the module 12 amaintaining command (OM) for the relay 2. The commands OF and OM alsocomprise the characteristics of the relay 2 and are processed in thecalculation means 123 jointly with the value of the level of the batteryvoltage V_(A), increased by the analogue digital converter 4. V_(A) is afunction of time V_(A)=V_(A)(t). The calculation means 123 thuscalculates the cyclic ratio RC of the pulse duration modulation means122 in the following manner.

In a first version (see FIG. 2),

between to and t1, in contacting phrase, thus during Δt:RC=1after t1, in maintaining phase, and if a release command has notintervened (at t2 in FIG. 2)RC=V _(M) /V _(A)(t).

Thus the maintaining command of the relay is modulated over timeaccording to the power supply and the maintaining voltage when onlymaintaining is necessary. The relay is supplied with power under anaverage voltage equal to V_(M) which reduces its thermal dissipation bythe quantity:Q=(V ² _(A) −V ² M)/Rassuming that R represents the resistance of the coil of the relay.

In a second more sophisticated version;

between to and t1, during ΔtRC=V _(C) /V _(A)(t)

between t1 and t2RC=V _(M) /V _(A)(t)with similar consequences to those previously seen in the dissipation ofenergy from the relay.

If the battery delivers a sufficiently stable voltage V_(A) it ispossible to simplify and admit into the calculations that the voltageV_(A)(t) is equal to a constant average value V_(A)moy.

The means 123 transforms the commands OF and OM by changing the cyclicratio RC value for the means 122. In order to open the relay 2, thecontrol module sends a release command to the module 12, thus to themeans 123, which simply cancels the cyclic ratio RC which has the effectof opening the switch I.

Upon a micro power cut being detected by the circuit 11 the module 11sends a closure command OF to the module 12 if the relay 2 was subjectto an OF or OM command. This makes it possible to avoid the risk of notbeing able to close the relay, the maintaining voltage beinginsufficient for that.

Another embodiment will be described hereinunder with reference to FIG.3. The circuit ASIC (“Application Specific Integrated Circuit”), thecircuit UCC (control-command unit) and the oscillator OSC permitimplementation of the process of the invention.

The control-command unit (UCC) has the means 123 and those of the module11 except that provided by the micro power cut detection circuit 111.

The module 11 is integrated in the circuit ASIC as well as N means 122for pulse duration modulation MID, intended to control N relays. Eachmodule corresponding to MID1, MIDi . . . , MIDN, has a register RCUcontaining a number of 8 bits equal to 256 times the cyclic ratio RC.The oscillator OSC of frequency F increments an 8 bit counter of whichthe value is compared to the content of the RCU register. In the eventof equality, with reference to FIG. 4, the output signal MIDi serving tocontrol a relay i is set to zero. In the event of overflow (OVF) of the8 bit counter, this same signal is set to 1. An MID circuit of frequencyF times 256 has thus been produced.

If F 25 kHz, the cycle of the MID is about 10 milliseconds.

Using a comparator CMP, a circuit DMC compares the battery voltage witha reference function in order to detect micro power cuts. When a micropower cut occurs the output of the module MID i is set to 1 so as toshort-circuit the MID i circuit if this circuit is in the phase ofmaintaining the relay i, information being available in the register RC.

1. Process for controlling electromagnetic relays (2) comprising atleast one contact, controlled by a voltage or current supply (1),characterised in that the control is modulated according to the voltageor current supply and to the contacting voltage which is sufficient toclose the contact of the relay (2), and is modulated according to thevoltage or current supply and to the maintaining voltage which issufficient to maintain this closure.
 2. Device (10) for controllingelectromagnetic relays (2) from a voltage source (1) implementing theprocess of claim 1, characterised in that it has a module (12) foradapting the power supply of the relay and a control module (11) tocontrol the power supply-adapting module.
 3. Device as claimed in claim2, wherein the control module (11) has means (112) to control theduration of operation of the power supply-adapting module (12) duringcontacting of the contacts, a duration at the end of which it mustcontrol the maintaining of the contacts.
 4. Device as claimed in one ofclaims 2 and 3, wherein the control module (11) has a module (111) fordetecting micro power cuts.
 5. Device as claimed in one of claims 2 to4, comprising an oscillator (13) connected to the power supply-adaptingmodule (12), which comprises a calculation means (123) and a means (122)for pulse duration modulation (MID) of the supply voltage.
 6. Device asclaimed in one of claims 2 to 5, comprising a memory (113) storing thecharacteristics of the relay (2).
 7. Specific integrated circuit (ASIC)comprising at least one pulse duration modulation means (122), themodulation means (122) being controlled by a control-command unit (3)programmed for modulating the power supply of at least oneelectromagnetic relay 2 according to the process of claim
 1. 8. Circuitas claimed in claim 7, characterised in that it further comprises acircuit (DMC) for detecting micro power cuts.
 9. Circuit as claimed inclaim 8, wherein the micro power cut detector circuit, upon occurrenceof a micro power cut, controls a contacting voltage on the relays withcontrolled maintaining voltage.